Identification of transmission of ratio distortion regions on the beef cattle genome and their association to bull and cow fertility


Source: Beef Farmers of Ontario

Executive Summary

Although feed costs are a major factor influencing the profitability of beef production, successful reproduction in the cow-calf sector is a primary driver affecting profitability. The number and percentage of cows successfully bred during the breeding season is a major factor influencing the profitability of the cow-calf operation. Bull fertility plays a key role in the success of calf production. Identifying bulls with superior fertility and with superior feed efficiency could significantly impact cow-calf production efficiency. However, it is important to understand the relationships between fertility and feed efficiency to avoid undesirable consequences of selection for a single trait as the beef cattle industry is beginning to more aggressively select animals for improved feed efficiency.

The main objective of the project is to discover new regions of the genome and the genes located in them that affect reproduction. These new genome signals or regions will be called “transmission ration distortion (TRD)” in the proposed project. TRD occurs when one of the two alleles from a heterozygous locus is preferentially transmitted to the progeny. This phenomenon typically causes a departure of the expected Mendelian inheritance ratios in the offspring. TRD has been reported in a broad range of organisms including plants, insects, fish, birds, and mammals. However, little is known of its effects on livestock species. Several biological mechanisms can cause TRD, including the preferential transmission of one of the two alleles carried by a heterozygote parent to the zygote at the time of fertilization, also known as meiotic drive, as well as embryo or fetal failure or differential viability during early neonatal life under a given genotype.

In this study the analysis of TRD will be used to discover new regions of the genome and the genes located in those regions that may have an effect on reproduction. Such regions, if they affect male and female fertility through embryonic or early calf mortality, are expected to change the distribution of genotypes among progeny in relation to the genotypes of the parents. Once TRD regions have been identified, their phenotypic effects will be analyzed integrating structural and functional genomic data through associations using the new bovine genome assembly ARS-UCD1.0 that is currently being developed with fertility phenotypes or genetic evaluations (e.g. sire conception rate, non-return rate and semen quality traits) and functional studies (gene ontology and biological pathways analysis).

In addition, the association between SNP located in the genes with TRD and feed efficiency traits will also be examined in order to study possible correlation between feed efficiency traits and fertility in young beef bulls. The proposed project will identify genomic regions with TRD as well as the key regulator genes and functional SNP affecting fertility and reproduction in different beef cattle breeds and its correlation with feed efficiency in young bulls. In order to identify the causal mutations, further validation of the most promising genes found will be investigated sequenceing two groups of animals with extreme phenotypes (fertility traits).

Completion Date: 2018


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